CBSE Sample Papers for Class 12 Biology Paper 2

CBSE Sample Papers for Class 12 Biology Paper 2 are part of CBSE Sample Papers for Class 12 Biology. Here we have given CBSE Sample Papers for Class 12 Biology Paper 2.

CBSE Sample Papers for Class 12  Biology Paper 2

Board	CBSE
Class	XII
Subject	Biology
Sample Paper Set	Paper 2
Category	CBSE Sample Papers

Students who are going to appear for CBSE Class 12 Examinations are advised to practice the CBSE sample papers given here which is designed as per the latest Syllabus and marking scheme as prescribed by the CBSE is given here. Paper 2 of Solved CBSE Sample Paper for Class 12 Biology is given below with free PDF download solutions.

Time: 3 Hours
Maximum Marks: 100

General Instructions:

• There are total 26 questions and five sections in the question paper. All questions are compulsory.
• Section A contains question number 1 to 5, Very Short Answer Type Questions of one mark each.
• Section B contains question number 6 to 10, Short Answer Type Questions of two marks each.
• Section C contains question number 11 to 22, Short Answer Type Questions of three marks each.
• Section D contains question number 23, Value Based Question of four mark.
• Section E contains question number 24 to 26, Long Answer Type Questions of five marks each.
• There is no overall choice in the question paper, however, an internal choice is provided in one question of two marks, one question of three marks and all three questions of five marks. An examiner is to attempt any one of the question out of the two given in the question paper with the same question number.
• No. of printed pages are three.

SECTION-A

Question 1.
Any type of failure of testes to descend into the scrotum induces sterility in human males. Explain.

Question 2.
Phenomenon of DNA replication has a semiconservative nature. Explain the statement.

Question 3.
Mother’s milk is often termed as the most appropriate food for a new born infant. Give reason.

Question 4.
It is now possible to produce multiple copies of even a very small DNA template. Mention the fact how it happens.

Question 5.
Eichhornia crassipes is often nicknamed as ‘Terror of Bengal’. Justify.

SECTION-B

Question 6.
Any abnormal arrangement of one or more chromosomes in a body is known to be chromosomial disorder. Both Down’s syndrome and Klinefelter’s syndrome are one such type. Cite the differences between the nature and symptoms of the two.

Question 7.
What do you mean by the term ‘standing crop’ in an ecosystem? Draw a pyramid of biomass, when a small standing crop of phytoplanktons supports a large standing crop of zooplanktons in the sea.                OR

1. Compare the grazing food chain and detritus food Chain in terms of origin.
2. Which among the two is the major contributor to energy flow in aquatic ecosystem?

Question 8.
The excreta (dung) of cattle is used for the generation of biogas in many areas. Mention the function performed by it.

Question 9.
Radhika went on a school trip to some garden and started sneezing after she reached there. In the evening when she came back home, she was feeling all fine. What could be the reason behind her such condition? Also tell the type of antibody being produced by the body as a response against it.

Question 10.
What contribution were made by TH Morgan as a geneticist in the field of genetics? Give any two of them.

SECTION-C

Question 11.
Answer the question given below
(1) Identify the parts labelled A, B, C and D in the diagram of a seed.

(2) State the reason behind the fact that why some fruits are seedless i.e. contain or empty or non-viable seeds with the help of a suitable example.

Question 12.
Which three hypothesis explains the logic behind the fact that the tropics shows greatest level of species richness?

Question 13.
Explain some major ways to prevent and control the drug and alcohol abuse among the adolescents.

Question 14.
State the importance behind testing of new plant varieties in a geographically vast country t like India.

Question 15.
(1) Eco RI is a well known restriction endonuclease. How it is named so? Give details.
(2) Why it is essential to have a selectable marker in a cloning vector?

Question 16.
Explain the process behind a Polymerase Chain Reaction (PCR).

Question 17.
Write a note on the following.
(1) Mycorrhiza
(2) Cyanobacteria
(3) Nitrogen-fixing Bacteria

Question 18.
The base sequence in one of the strands of DNA is TAGCATGAT.

1. Give the base sequence of the complementary strand.
2. How are these base pairs held together in a DNA molecule?
3. Explain the base complementary rule. Give the name of the scientist who framed this rule.

Question 19.
A couple visited a Doctor to know whether their foetus (unborn child) is suffering from any chromosomal disorder which is incurable. What suggestions would you give under such circumstances?

Question 20.
(1) Describe all the barriers of innate immunity.
(2) When do innate immunity become active?
OR
Diagrammatically trace the life cycle of a malarial parasite in the human body when bitten by an infected female Anopheles.

Question 21.
The base sequence of one strand of DNA is TACTAGGAT.

1. Write the base sequence of the RNA got after transcription of the given sequence.
2. What is the distance maintained between the two consecutive pairs in the DNA molecule?
3. Who contributed the base complementary rule?

Question 22.
Give diagrammatic representation of Miller’s experiment.

SECTION-D

Question 23.
Anil was waiting at a bus stop. Many passengers along with their kids were on their way to school. A bus came and painted the children with black smoke being ejected from the exhaust pipe. Anil immediately stopped the bus and called the conductor and driver to show what they had done. Passengers waiting in the bus stop supported Anil, while those on board became restless for being delayed.

1. Why are children more affected by vehicle exhausts?
2. Cars are seen with Bharat stage IV stickers. What does it imply? .
3. How do catalytic converters reduce vehicular gas emission?
4. What value did Anil promote through his action?

SECTION-E

Question 24.
Examine the flowchart given below and identify the name of the hormones involved at each stage inside a female body. Also explain the roles performed by each of them.

OR
Discuss the post-zygotic events in human female that leads to a process of implantation in uterus .with a neat and a well labelled diagram.

Question 25.
State the aim and describe Messelson and Stahl’s experiment in detail.
OR
(1) What did Messelson and Stahl observe when:
(a) They cultured coil in medium containing ¹⁵NH₄C1 for a few generations and centrifuged the content?(b) They transferred one such bacterium to the nomal medium of NH₄C1 and cultured for two generations?
(2) What did Messelson and Stahl conclude from their experiment? Explain only with the help of the diagrams.
(3) Which is the first genetic material? Give reasons in support of your answer.

Question 26.
Explain the following terms (with example)

1. Migration
2. Aestivation
3. Hibernation
4. Diapause

OR
Cite the difference between the following terms used for organism and its population.

1. Immigration and Emigration j
2. Ectomycorrhizae and Endomycorrhizae
3. Population and Community
4. Ecotone and Edge Effect
5. Keystone Species and Critical Link species.

Answers

SECTION-A

Answer 1.
The higher temperature in the abdomen of the human males is not suitable for the development of the sperms and induces sterility in human males.

Answer 2.
DNA describes the mechanism where each DNA molecule produces two copies each containing one of the original strand (parental) and one newly synthesised strand. This explains semi­ conservative nature of replication of DNA.

Answer 3.
Mother’s milk provides immunity as it contains abundant IgA antibodies to protect the newly born child from foreign antigens and other harmful substances.

Answer 4.
DNA is able to multiply itself in host organism and produce multiple copies of its template when an alien DNA is linked with the origin of replication.

Answer 5.
Eichhornia crassipesis often nicknamed as ‘terror of Bengal’ because it grows very fast in the water-bodies and depletes the dissolved oxygen, disturbing the complete ecosystem dynamics of the water-body.

SECTION-B

Answer 6.

	Down’s Syndrome	Klinefelter’s Syndrome
Nature	Genetic disorder which arises due to trisomy copy of the chromosome number 21 i.e. (2/7 + 1).	Genetic disorder which arises due to the presence of additional copy of X-chromosome resulting into a karyotype of 47 i.e. (XXY).
Symptoms	Individuals with this abnormality are short statured with small rounded face, have furrowed tongue and partially mouth. Palm is broad with characteristic palm crease. Physical psychomotor and mental development is retarded	Overall development of masculine character occurs. Feminine development (development of breast) is also expressed and individuals are sterile.

Answer 7.
Standing crop is measured as the biomass of living organisms or the number in a unit area of a particular trophic level. The biomass of a species is expressed in terms of fresh or dry weight

OR
(1) Grazing Food Chain (GFC) begins from producers or green plants whereas, Detritus Food Chain (DFC) begins from remains of dead plants such as leaves, bark, flowers and dead remains of animals.
(2) In aquatic ecosystem, grazing food chain is the most or major contributor of energy flow than detritus food chain.

Answer 8.
Cattle excreta (dung) is used for the generation of biogas because it is rich in methanogens. Methanogens easily digest cellulosic material present in rumen of cattle and play an important role in nutrition of cattle, e.g. Methanobacterium.

Answer 9.
Radhika, must had suffered from some kind of allergy either from the dust or may be by the pollen grains of the flowers etc. Such substances are called allergens. Our body eventually produces IgE antibodies as a response against such allergens.

Answer 10.
T.H. Morgan, an American genetist was awarded with a Nobel Prize in the year 1933. Two contributions he made in the field of genetics, are as follows:

1. Found Drosophilla melanogaster (fruit fly) and proved it as a better model for experiments on genetics due to their easy rearing and ability to multiply throughout the year.
2. Had established the presence of genes over the chromosomes.

SECTION-C

Answer 11.
(1) A— Seed
B — Thalamus
C — Endoscarp
D — Mesocarp.
(2) Some fruits are seedless because they are produced without fertilisation and are called parthenocarpic fruits, e.g., Banana.

Answer 12.
Three hypotheses for explaining the greatest level of species richness in tropics are:

1. Tropics rich in species because the temperate regions were subjected to the frequent glaciation, while tropics remained relatively undisturbed for millions of years. Thus, they got long time for species diversification.
2. Tropical environments are more constant and predictable. Therefore, it promotes niche specialisation and leads to the greater diversity. Thus, tropics are more species rich.
3. Tropics have more solar energy exposure, which contributes to the higher productivity and indirectly leads to the greater diversity.

Answer 13.
Some important measures that should be taken for the prevention and control of drugs and alcohol abuse among adolescents are:

1. Avoid undue peer pressure.
2. Education and counselling.
3. Seeking help from parents and peers,
4. Looking for danger signs.
5. Seeking professional and medical help.

Answer 14.
Before the generation of new plants through plant breeding programs, plant needs to be evaluated for their yield and other agronomic traits of quality, disease resistance, etc.
The testing is done on the farmer’s field for atleast three growing seasons, at different locations in the country representing all the agroclimatic zones, where the crop is usually grown. The material is thus, evaluated in comparison to the best available local crop cultivar known as a check of reference cultivar and finally the product is released.

Answer 15.
(1) EcoRI is derived from Escherichiacoli RY 13. It is a named as follows:

• The capital letter E comes from Escherichia (genus).
• The letter C comes from Coli (Species).
• The letter R comes from RY13 (strain). .
• The Roman number I indicates it was the first enzyme isolated-from the bacterium E. coli RY 15.

(2) Selectable marker is essential in cloning vector because it identifies and eliminates non­transformants and selectively permits the growth of transformants.

Answer 16.
PCR (Polymerase Chain Reaction) is a reaction in which amplification of specific DNA sequences is carried out in vitro.
The process of PCR is given below:
(1) Denaturation c/s DNA (double stranded DNA) is denatured and separated by applying high temperature of 95°C for 15 s.
(2) Annealing: Two sets of primer are added which anneal to the 3 end of each separated strand. These primers act as the initiators of replication.
(3) Extension in this step, DNA polymerase extends the primers by adding nucleotides complementary to the template provided in the reaction.

• A thermostable DNA polymerase i.e. taq polymerase is used in the reaction, which can tolerate the high temperature of the reaction.
• All these steps are separated many times to obtain several copies of desired DNA. (I)

Answer 17.
(1) Mycorrhiza: It is a symbiotic association between fungus and the roots of higher plants.
The fungus absorbs water and minerals from the soil and passes them on to the plant. The carbohydrates synthesised by the plant are absorbed by the fungus.

(2) Cyanobacteria: They are autotrophic microbes found in aquatic and terrestrial environment. They help in nitrogen fixation, e.g. Anabaena and Nostoc. Cyanobacteria are used in paddy fields as an important fertiliser.

(3) Nitogen-fixing bacteria: These are either symbiotic bacterium like Rhizobium or free- living bacteria, Azospirillum and Azotobacter, which fix atmospheric nitrogen and enrich the soil nutrients.

Answer 18.

1. ATCGTACTA
2. Base pairs are held together by weak hydrogen bonds. Adenine pairs with Thymine by two H-bonds and Guanine pairs with Cytosine forming three H-bonds.
3. Base complementarity rule for a double-stranded DNA states that the ratios between Adenine and Thymine and Guanine and Cytosine are constant and equal to one. Ervin Chargaff framed this rule.

Answer 19.
If the foetus is suffering from any chromosomal disorder that is incurable, the couple should go for MTP (Medical Termination of Pregnancy). The suggestion can be given as:

1. MTP is considered relatively safe only during the first trimester, i.e. upto 12 weeks of pregnancy.
2. Second trimester abortions are considered to be much more risky.

Answer 20.
(1) Barriers of innate immunity are as follows:

• Physical Barriers such as skin, mucous, coating of the epithelium, lining of respiratory, gastrointestinal and urogenital tracts.
• Physiological Barriers such as, acid in stomach, salvia in the mouth, tears from eyes.
• Cellular Barriers: Certain types of leukocytes (WBC) of our body like, Polymorpho­nuclear leukocytes (PMNL-neutrophils), monocytes, natural killer cells and macrophages
• Cytokine Barriers: Proteins called interferons being secreted by Virus infected cell,

(2) Innate immunity in an individual becomes active as soon as ahy foreign material (virus, bacteria and pathogen) enters the body.

Answer 21.
(1) AUGAUCCUA
(2) 3.4 A or 0.34 nm.
(3) Chargaff contributed the base complementary rule.

Answer 22.

SECTION-D

Answer 23.

1. Height of the smoke emitted from exhaust pipe is closer to the height of the children.
2. It indicates that the vehicles comply with the new auto fuel policy. At present, vehicles complying Euro IV or equivalent BS-IV norms are to apply in the identified 11 cities, rest of the country to follow Euro 1I/BS-III norms.
3. In these devices, platinum, palladium and rhodium are used as catalysts. As the exhaust passes through the converter, unbumt hydrocarbons are converted into CO, and H_r Carbon monoxide and nitric oxide are changed into C0₂ and N, gas respectively. Vehicles fitted with such equipment should run on unleaded petrol only. Since, lead in petrol inactivates the catalysts.
4. Anil shows alertness, responsibility and firmness in tackling a problem. He expresses boldness towards environment consciousness.

SECTION-E

Answer 24.
A rapid release of Luteinsing Hormone (LH) ruptures Graafian follicle and release ovum by the process of ovulation in the initiation of the process in human females.Corpus luteum then secretes a large amount of progesterone hormone that is known to be essential for the maintenance of the endometrium (a uterine layer) required for the implantation of blastocyst leading to pregnancy.

Placenta produces several hormones like human Chorionic Gonadoptropin (hCG), human,Placental Lactogen (hPL). Relaxin is the another hormone being produced during the later phase of pregnancy. Levels of other hormones like oestrogens, progesterone, cortisol, prolactin – and thyroxine and thyroxine also increases, which is essential for supporting the foetal growth,metabolic changes in mother and maintenance of pregnancy.

Parturition signals the originate from the fully developed foetus the placenta induces mild uterine contractions which triggers the release of oxytocin hormone from pituitary gland. Oxytocin acts on the uterine muscle causing stronger uterine contractions.
OR
During post-zygotic events sperm and ovum gets fused together to form zygote.
The events which follows are:

1. Mitotic division starts in zygote. This is called cleavage. After repetitive division, it forms 2,4,8, 16 daughter cells called blastomeres. Embryo 8-16 blastomeres forms morula which continues to divide and transform into blastocyst.
2. The blastomeres in blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast is called inner cell mass.
3. Trophoblast layer then gets attached to endometrium (innermost layer of uterus) and inner cells mass gets differentiated as embryo.
4. After attachment, uterine cells divide rapidly and cover the blastocyst.
5. As a result, blastocyst becomes embedded in the endometrium. This is called implantation leading to pregnancy.
   

Answer 25.
Messelson and Stahl in 1958, aimed to prove that DNA replicates in a semi-conservative fashion. This semi-conservative DNA replication suggests that, after the completion of replication, each DNA molecule will have one parental and one newly-synthesised strand. The process of experiment conducted by them is as follows:
Description of the experiment:
(1) They grew E. coli in a medium containing ¹⁵NH₄C1, (¹⁵N is the heavy isotope of nitrogen) for many generations.
As a result, ¹⁵N got incorporated into newly synthesised DNA. This heavy DNA can be differentiated from normal DNA by centrifugation in caesium chloride (CsCl) density gradient.
Then they transferred the cells into a medium normal ¹⁴NH₄C1 and took the samples at various definite time intervals as the cells multiplied.
(2) The extracted DNAs were centrifuged and measured to get their densities. The DNA extracted from culture after one generation of transfer from the ¹⁵N to ¹⁴N medium showed an intermediate hybrid density.
The DNA extracted from culture after two generations showed equal amounts of light DNA and hybrid DNA.
OR
(1)
(a) Messelson and Stahl observed that the ¹⁵N was incorporated into the newly synthesised strand of DNA and also other nitrogen containing compounds. This heavy DNA could be distinguished from the normal DNA by centrifugation in a cesium chloride (CsCl) density gradient.

(b) DNA from such bacterium had a hybrid or intermediate density, one generation after the transfer from ¹⁵N to ^l4N. After another generation, it composed of equal amount of this hybrid DNA and of light DNA.

(2) Messelson and Stahl concluded that the replication of DNA is semiconservative.

(3) RNA is the first genetic material. This is because:

• Essential life processes have evolved around RNA.
• It acts both as catalyst and genetic material.

Answer 26.
(1)Migration: In this, organism temporarily moves away from the stressful habitat to a more hospitable area and return when stressful period is over, e.g., birds undertake long distance migration during winter.

(2) Aestivation: It is acquired to avoid summer-related problem like heat and desiccation. For example, some fishes undergo aestivation.

(3) Hibernation: Some animals avoid the winter stress by escaping in time, e.g., bears undergo hibernation during winter.

(4) Diapause: It is a stage of suspended development during unfavourable condition e.g., many zooplankton species in lakes and ponds enter diapause.

OR

(1)

Immigration	Emigration
It is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.	It is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

 (2)

Ectomycorrhizae	Endomycorrhizae
In this, the fungal mycelium forms a net outside the root.	In this, the fungal mycelium dwells inside the roots.

(3)

Population	Community
It is a group of individuals of a single species found in an area.	It is a group of individuals of different species found in an area.
All the individuals are morphologically and behaviourally similar.	Different individuals are morphologically and behaviourally dissimilar.

(4)

Ecotone	Edge Effect
1. An area of transition between the two biotic communities or ecosystem.	1. It is the characteristic or specific species composition found at ecotone or community boundary
2. It is characterised by the presence of species of both the communities.	2. It is characterised by higher number of species, the increased density and certain specific edge species.

 (5)

Keystone Species	Critical Link Species
1. They are non-dominant species, which maintains the characteristics and structure of a community.	1. They are non-dominant species, which are important for the survival and support of network species.
2. They acts as a component of biological control and provide food in the period of scarcity.	2. They function as pollinators, dispersing agents, nutrient circulators, etc.

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